An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit which communicates with a fixed base station or access point that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the base station or access point. When the mobile unit moves out of range of one base station or access point, it may connect or “handover” to a new base station or access point and starts communicating with the wired network through the new base station or access point.
In comparison to infrastructure-based wireless networks, an ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of the nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multihopping”) until the packets reach the destination node. As used herein, the term “multihop network” refers to any type of wireless network which employs routing protocols among nodes which are part of a network. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination. Nodes in the ad hoc network use end-to-end path metrics to select a path, from the multiple path options to any destination. The path metrics are generally sum of the individual link metrics along the path.
A wireless mesh network is a collection of wireless nodes or devices organized in a decentralized manner to provide range extension by allowing nodes to be reached across multiple hops. In a multi-hop network, communication packets sent by a source node can be relayed through one or more intermediary nodes before reaching a destination node. A large network can be realized using intelligent access points (IAP) which provide wireless nodes with access to a wired backhaul.
A multi radio communication device supports two or more different wireless interfaces. The wireless interfaces, for example, can provide interfaces to different networks or alternatively can provide interfaces to different channels within a network. For example, a multi radio cellular telephone can provide Bluetooth communications and/or can support wireless fidelity (Wi Fi) along with its cellular data network.
A multi radio node within an ad hoc or mesh network can include multiple different radio modules supporting one or more channels and/or one or more communication protocols. (e.g., one radio module which complies with the Institute of Electrical and Electronics Engineers (IEEE) 802.11(a) standard, another radio module which complies with the IEEE 802.11(g) standard, and possibly another radio module which complies with the IEEE 802.11(b) standard, etc.). Each radio module typically has its own physical (PHY) layer, and its own medium access control (MAC) layer. A routing module which manages routing for the multi radio node is typically implemented above the MAC layer and potentially can run over multiple radios.
The IEEE 802.11 PHY specification permits the simultaneous operation of multiple non-overlapping channels. For example, three non-overlapping channels in the 2.4 GHz band can be simultaneously used. The IEEE 802.11a specification allows up to twelve non-overlapping channels in the 5.0 GHz band. By deploying multi-radio routers in wireless mesh networks and assigning the radios to non-overlapping channels, the routers can communicate simultaneously with minimal interference in spite of being in direct interference range of each other. Therefore, the capacity of wireless mesh networks can be increased.
The mesh network architecture is broadly composed of two processes: neighbor discovery and reactive routing. Neighbor discovery uses hello messages to determine neighbors and proactively propagate Internet Access Point (IAP) connectivity information. Reactive routing has many messages (e.g. route request (RREQ), route reply (RREP), route error (RERR), etc.) related to route discovery, route maintenance, and route binding.
To accommodate multiple radio operation, an enhancement to the mesh network architecture includes a node identification (ID) in hello messaging and in the neighbor table. This node ID is used to identify messages received from multiple radio interfaces as being from the same mesh node.
The availability of multiple radios could be used to increase throughput by using alternate channels to receive and forward mesh traffic. Accordingly, there is a need for a method and apparatus for intelligently selecting communication links in a multi-radio wireless communication system to increase system throughput.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.